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Re: Reliable after-change-functions (via: Using incremental parsing in E

From: Stefan Monnier
Subject: Re: Reliable after-change-functions (via: Using incremental parsing in Emacs)
Date: Mon, 30 Mar 2020 23:10:57 -0400
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/28.0.50 (gnu/linux)

> IOW, our goal is not to build the syntax tree, it's to give
> tree-sitter enough information to allow us to fontify the part that's
> about to be displayed.  We need to have tree-sitter play by Emacs
> rules, not teach Emacs to play by tree-sitter rules.

IIUC, tree-sitter starts by parsing the whole buffer anyway, and then
keeps the parse tree up-to-date in response to buffer changes.

Its algorithm is tuned so that the time needed to update the tree is
more or less proportional to the size of the change.

So jit-lock/font-lock doesn't need to pass any part of the buffer to
tree-sitter: tree-sitter already has the buffer's content and we can
assume its already parsed.  What emacs-tree-sitter's proposed
tree-sitter-highlight does is provide a function which takes
a START..END, then finds which part of the existing parse tree cover
that region and "reads the tree" to fontify the corresponding text.


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